This invention relates to novel tricyclic erythromycin derivatives. The compounds of this invention are useful as antibiotic agents in mammals, including man, as well as in fish and birds. The compounds of the present invention are broad-spectrum macrolide antibiotics that are effective against infections caused by certain gram-positive and gram-negative bacteria as well as protozoa. Various derivatives of erythromycin A useful as antibiotic agents are referred to in U.S. patent application Ser. No. 60/049,349, filed Jun. 11, 1997, and U.S. application Ser. No. 60/046,150, filed May 9, 1997, both of which are incorporated herein by reference in their entirety, and in U.S. patent application Ser. No. 60/063676, entitled "9-Amino-3-Keto Erythromycin Derivatives", (Yong-Jin Wu), filed Oct. 29, 1997, which is incorporated herein by reference in its entirety.